Use sodium bicarbonate to bring the PH up to about 6 (not higher).
Every NAD+ is different so there isn’t a standard amount that needs to be added. I would start by adding half of your sterile saline (or BAC water for SQ) wait until the vial is fully reconstituted, then test the PH. You want a target of 6, I have read that NAD degrades quickly at PH higher than about 6.5. If the PH is low, add a couple of units of SB then test again. Keep adding SB and testing until you achieve your target PH (keeping track of how much you added) then add the rest of your saline/BAC water, Also, remember to put a vent needle in your vial, its going to bubble a lot.
When you reconstitute your next vial the amount of SB you need to add should be about the same as the amount you added to your first vial.
edited to remove the link to Lidocaine OP was looking for Sodium Bicarb