Depends how badly you want to make this happen. You can always refuse to pay in fiat but you may want to try being nice first.

"Hi, I am writing to inform you that I have taken a job that pays me in Bitcoin only. Seeing as my income will be solely denominated in Bitcoin going forward, I would like to pay my rent in Bitcoin as well. Please let me know if you are open to this option."

If he says no then say "ok, I understand I will uphold my end of the lease and continue to pay in fiat but I will not be renewing unless given an option to pay in Bitcoin".

It is very costly for a landlord to lose a good tenant. Even in markets with low vacancy keeping the same tenant base if they are high quality tenants is always better than incurring the cost of touching up the space and looking for new tenants that might end up being deadbeats and not pay rent. Landlords don't usually want to take this risk unless they think they can get significantly higher rent from the new tenant.

If he still doesn't capitulate you can just stop paying rent and tell him you will pay in bitcoin but not fiat. If he is adamant on fiat he can evict you and try to collect in court (major pain in the ass). Obviously this wouldn't be your first play.