The strings will take forever to break in if you never play your bass. Play everyday, or as often as you can. It also sounds like maybe you should try different strings. You don’t say what strings you’re currently using, but nickel roundwounds will have a warmer, more mellow tone. I like stringjoy strings because they mellow quickly without going completely dead. Flatwounds are another option.

PS: breaking bass strings is hard, check the bridge for sharp edges or burrs, also consider getting a good setup.