Check first that your tablet is a cellular model. On an iPad, Settings → General → About shows an EID and an IMEI on cellular models; Wi-Fi-only models show neither and cannot use an eSIM.
On an iPad
- Settings → Cellular Data → Add eSIM.
- Scan the QR code, or choose Enter Details Manually.
- Turn on Data Roaming for the new line once you are abroad.
On an Android tablet
- Settings → Network & internet → SIMs → Download a SIM instead [Samsung: Connections → SIM manager → Add eSIM].
- Scan the QR code and follow the prompts.
A tablet is a good place to use a large data plan, because tethering from it is usually more reliable than from a phone that is also handling your calls.