Make and model router (or modem/router)?
Do you have administrative access to your home network router?
The router's User Guide/Manual should provide the necessary procedure and the accompanying set up screens.
However, all is moot if you do not have administrative rights to the router's configuration screens.
And there may be other factors involved - firewalls perhaps.
Here is a reference link that should help you work out the overall process needed to setup Minecraft port-forwarding.
https://www.noip.com/support/knowledgebase/how-to-host-and-configure-a-minecraft-server-with-no-ip/
More specifically using a Linksys router as an example:
https://portforward.com/linksys/
Check the above links and then google for similar links using search terms and phrases that are a closer match to your network environment.
The problem could be just some configuration error of omission or commission.