Ssl certificate on isp manager problem

Does anyone know how to install comodo ssl certificate to isp manager ?
Although in plesk is very easy , in isp is hard. I contacted with sectigo and isp and they want money to install it. I found some guides on google but with no luck.
A very kind assistant from comodo tried to solve the problem but he was asking me for a private key and the only things i had after my order was 2 files.
Any help ???