How do I lock my apps?

[BingHui]

I'm sending my phone for repair soon and would like to lock apps that contain sensitive information like gallery and messaging apps. I can't seem to find the settings for that. Does anyone know how I can go about doing that? I would like to have an additional layer of security on top of maintenance mode 

[JP19]

Hi, to be honest the only safest way is to factory reset, when comes to protection of sensitive data.

[NoUseForANickname]

Use maintainence mode if your phone allows it.