Two questions about repayment. Please help!

Looks like my loans are still in forbearance. I have two questions:

1. Is it a dumb idea to pay a chunk off now? Any downside to doing this while still in forbearance? Like if I wanted to pay $5-$10k?

2. Where on the website when making a payment can I designate I want the big payment to go toward principal only? Is there a box I check to indicate I want the payment to go toward the principal?

Sorry if these are weird questions. I just am not sure…

Thanks!