Custom ssl certificate

Hi, can anyone help me to implement custome SSL Certificate?

The company that I got the SSL cert from gave me 3 files
1 x thing called private key
1 x thing called csr
1 x thing called SSL-Certificate

This is not directly related to Nextcloud.

Which webserver are you using?
Search the web for this basic webserver issue.

I am using apache. In the NextCloudSnap

So just ssh into your snap and look /etc/apache

See https://github.com/nextcloud/nextcloud-snap/wiki/Enabling-HTTPS-(SSL,-TLS) as well.