Install a SSL certificate on Nginx server

We have a website for our dashboard : https://dashboard.domain.com/
The subdomain is located on ionos hosting company.
The server is located on upcloud company.

So the subdomain is pointing to the ip of upcloud server.

We purchased an SSL certificate on Ionos but we don't know how to install it on our upcloud server.
Ionos gave us these files:
dashboard.domain.com_private_key.key
dashboard.domain.com_seal.txt
dashboard.domain.com_ssl_certificate.cer
dashboard.domain.com_ssl_certificate_INTERMEDIATE.cer

Finally, we would prefer to use a free Let's encrypt server. By this way, we wouldn't have to pay every year the certificate.

We need an expert who can do this job as fast as possible.

We will test if https://dashboard.domain.com/ works fine before paying you.

We will give you access to our server through our computer with a zoom session.

Please send us your best offer if you are interested in this mission.