First of all, grapes as usually sold are first year grafts. They need about three years to bear fruit.
Secondly, they will likely survive if you prune them now, but given that you will get no grapes, and that it is a risk, you better wait until they are dormant again.
Are you planning to train them or are they just sprawling all over the place?
You should decide how you want to grow them right now. For table grapes I assume some sort of trellis.
If you did some training, keep at it and, in Winter, cut back to the vines that are trained.
If you didn't, learn about training techniques and train the shoot that is straighter/better aligned to the main trunk. The first few years are very important so, if you messed up, cut back to one dormant bud and start over next year.
Know that you can and should remove new shoots that you don't need and that you can also pinch the tips of new vines with little worry.