cleaning up low end energy build up in already finished mixes

I had to, very quickly, mix and "master" an album.

It's about to go into production and I feel like the album could be louder, but I think some low end energy is keeping it down.

I don't want to squash it, but I wonder if there's an easy way to work on the low end of a mix after it's been mixed, without killing it.

cleaning up low end energy build up in already finished mixes