1.Do you have access to the router’s web interface?
2.if yes, than login to it and write down the WAN IP displayed (public IP, that dosen’t start with 192.168… or 10.0…).
3.unplug the router from the power outlet and wait 5-10min.
4.power back on the router and check back the WAN IP.
Is it the same as the first one?
If yes, you are lucky; you have a fix WAN IP.
If isn’t, you have to use a DDNS service, like noIP. Google both terms to familiar yourself with this stuff. You should spend some time to learn about networking, because it’s not rocket sience and it will help you the entire life in many situations.
Here’s a good free course:
https://www.netacad.com/courses/networking-basics
You have 30 days to get back online, but you start to loose data after 4 hours of downtime.