Check if entity is being tracked by Entity Framework context

I have a code block which checks whether an entity is being tracked by my context. If it is, I need to detach it. This works for a given T type.

public virtual async Task<bool> InsertOrUpdate(TE entity)
{
    if (entity.Id == 0 || entity.Id == ModelState.New)
    {
        // attach new entity
        _context.Entry(entity).State = EntityState.Added;
    }
    else
    {
        // Sometimes when you want to update a detached entity, before attempting to attach it (by setting the .State property),
        // you first need to make sure the entity isn't already attached and being tracked. If this is the case, the existing entity
        // needs to be detached, and the updated entity, attached.
        var attachedEntity = _context.ChangeTracker.Entries<TE>().FirstOrDefault(e => e.Entity.Id == entity.Id);
        if (attachedEntity != null)
        {
            // the entity you want to update is already attached, we need to detach it and attach the updated entity instead
            _context.Entry<TE>(attachedEntity.Entity).State = EntityState.Detached;
        }

        _context.Entry<TE>(entity).State = EntityState.Modified; // Attach entity, and set State to Modified.
        _context.Entry<TE>(entity).Property(o => o.CreatedUserId).IsModified = false;
        _context.Entry<TE>(entity).Property(o => o.CreatedDate).IsModified = false;
    }

    return await _context.SaveChangesAsync() > 0;
}

I now need to change the method so that it fetches all objects of type IEntity within the given T entity parameter and then do the same logic for each object found, but I'm having trouble with setting the ChangeTracker.Entries as I need to set the T type to the current selected type within the foreach. I have no idea how to do this.

public virtual async Task<bool> InsertOrUpdate(TE entity)
{
    //// Find all instances of IEntity within TE: 
    ////  * IF entity is new we set State to EntityState.Added (INSERT)
    ////  * IF entity is existing, we set State to EntityState.Modified (UPDATE)
    List<IEntity> found = FindAllInstances<IEntity>(entity);
    foreach (IEntity ent in found)
    {
        if (entity.Id == 0 || entity.Id == ModelState.New)
        {
            // attach new entity
            _context.Entry(entity).State = EntityState.Added;
        }
        else
        {
            // Sometimes when you want to update a detached entity, before attempting to attach it (by setting the .State property),
            // you first need to make sure the entity isn't already attached and being tracked. If this is the case, the existing entity
            // needs to be detached, and the updated entity, attached.
            var attachedEntity = _context.ChangeTracker.Entries<TE>().FirstOrDefault(e => e.Entity.Id == entity.Id);
            if (attachedEntity != null)
            {
                // the entity you want to update is already attached, we need to detach it and attach the updated entity instead
                _context.Entry<TE>(attachedEntity.Entity).State = EntityState.Detached;
            }

            _context.Entry<TE>(entity).State = EntityState.Modified; // Attach entity, and set State to Modified.
            _context.Entry<TE>(entity).Property(o => o.CreatedUserId).IsModified = false;
            _context.Entry<TE>(entity).Property(o => o.CreatedDate).IsModified = false;
        }
    }

    return await _context.SaveChangesAsync() > 0;
}