this https://www.microsoft.com/surface/en-us/support/warranty-service-and-recovery/how-to-get-your-surface-ready-for-service?os=windows-10&=undefined should be helpful, specifically
Can I erase all my data manually before sending in my Surface?
Yes. The data on your Surface is erased as part of the service process. However, if you prefer, you can erase your data yourself before sending us your Surface.
To erase your data:
| Step 1: | Go to Start |
|---|---|
| Step 2: | Under Reset this PC, select Get started. |
| Step 3: | Select Remove everything. |
| Step 4: | Select Remove files and clean the drive. |