how do you twist a bowstring and when does it need to be done
Thanks

You press your bow down, pull the string off, and twist it. Normally this is done after you've broken in your new string and are putting it back to specs. I dont twist my strings very often, maybe for a peep alignment every now and then.

I write down a few important measurements (especially axle-to-axle) and twist my sting whenever it stretches more than 1/16", or when it gets out of time (or sychronization). Usually you only have to do this for the first couple hundred shots, but I check every month or so just in case.