There are generally 2 versions of this issue, the donation was just made and isn't showing up immediately or the donation was done more than a day ago and isn't showing up after waiting.
If the donation was just done usually clearing cache and cookies will fix it. You can send the participant these articles:
How Do I Reset my Cache and Cookies on Windows
How Do I Reset my Cache and Cookies on Mac
If it's been multiple days you can do a couple checks before sending them to DonorDrive.
If they have the email for the donor (or if it's them) go to their account on Extra-Life.org/admin and see if the donation is there under "Transactions". If not, it may have been done under a different email tied to the payment process used. IE if they use Paypal the donation will go under that email.
If the donation is a facebook donation there isn't really much to do. It has, in the past, taken a few days for those donations to sync so if it's been more than a week they'll need to go directly to Donor Drive.
After checking those things and if they all look correct, you can send them to https://www.donordrive.com/contact-us/ to contact Donor Drive directly and they can look at it further. Very rarely will participants or donors need to be sent to Donor Drive directly, so make sure to go through the steps and reach out to Zac or Ashley if you have questions about a participant's problem!