From the question I suppose you don't have any chem glassware nor knowledge, so you can do this:
1. Buy muriatic acid (35% is ok)
2. Put your methylamine bottle in a fridge to cool it down (but not freeze!)
3. Mix your cold methylamine with muriatic acid (add acid by small portions)
4. Check pH. If it is 7 or higher -> go to the step 3
5. Once you reached pH 6 or lower: boil out excess water (gentle boiling)