Possibly, most servicers allow payments to be directed to a specific loan!
When signing up for Changed, you should input the main account number that your servicer gives you -- You may see multiple individual loans under your account (These loans usually have some type of loan identifier which are a series of numbers or letters).
If you'd like to direct your payment to a specific loan Please input the loan identifier in the “loan Id” field under your loan information.
If you did this and still see payments applied to all your loans instead of targeting a specific loan. Please reach out to your loan servicer and request that all additional payments be applied to the loan Id you wish to target. In most cases, they will notate your account and this should correct the issue.