Advice on a correct dose of vitamin B12

[Gr8Nica]

Before I was taking 1000 mcg of B12 to maintain my levels of around 800. In September I started taking Metformin and I upped my dose to 2000 mcg knowing it lowers B12. Just had my levels checked and currently it is:

Serum vitamin B12 level 532 ng/L [160 - 800]

Any suggestions on what dosage should I be taking to take my level back to the top of the range?

[SeasideSusie Remembering]

If that was me I'd just add an extra 1000mcg a few days a week, maybe alternate days.