To be certain, list the available python versions using
python3 --version
With this confirmation, you can uninstall the version you do not want (3.7) by running:
sudo apt remove python3.7 #this removes only the python package
To remove the python package and any other dependant package which are no longer needed, run:
sudo apt autoremove python
If you also want to delete configuration and/or data files of python from Ubuntu, run:
sudo apt purge python
To remove all related python3.7 configuration, data files, and dependencies, run:
sudo apt autoremove --purge python