To record calls you can download ACR call recorder app from the play store.
To record calls on Mi A1 Follow the steps below:
1. Download the ACR call recording app from the play store
2. Then Follow the instructions from the app and allow all the access to the app as shown in the Image below
4. Then Tap the three bar on the top left of the app
5. There you will find the Enable option on the top.
6. Enable it and enjoy the app.
You can also check this video for more detailed information.
You can follow the steps below: