So want to From the admin the exact answer about what will if someone, unfortunately, send more than 0.001 BTC to 0.00499 BTC for mixing.
In general and according to their FAQ, any sent amount smaller than 0.005 and different from 0.001 will be considered as a donation.
If it was sent by mistake, you will have to contact their customer support for further assistance.
https://www.go-overt.com/#faq