Looks like you define it in a secret and tell helm where to look for it in additionalScrapeConfigs

If I will add service monitor ?

In rancher

I have installed mongodb cluster and mongo exporter and I need to take the info from the exporter to Prometheus

Here's the syntax for the scrapeconfig: https://github.com/prometheus-operator/prometheus-operator/blob/main/Documentation/user-guides/scrapeconfig.md