$1 is from like one day ago and has a lot of good advice in it.
Rehire-specific advice: generally need very little training in my experience, but ask how long they've been out and how long they worked. In the past 2 years or so there's actually been a good amount of changes to standard recipes- like hot chocolate's changed, making WC has changed, etc. Honestly you might want to just set aside time and have them tab through all the recipes so they can skim / catch any changes from when they worked. Ask them what their preference for training is - some will be like "I still remember everything" and treating them as a greenbean can feel condescending. Some will feel like "I don't remember a*nything* I definitely want to start from the ground up."