For a Form 8606, you would send it to the same IRS address as you would for a Form 1040.
That address is based on your state. Please visit the link provided below to find the address to send your Form 8606 into:
(As a side note- the IRS website will say it is for forms "1040 and 1040X"- do not mind that. It is the same address you will send your Form 8606 into).
https://www.irs.gov/uac/where-to-file-addresses-for-taxpayers-and-tax-professionals-filing-form-1040
I hope this information guides you in a positive direction!
