If the jre is installed on your machine properly then look for keytool in jre or in jre/bin
to find where jre is installed, use this
sudo find / -name jre
Then look for keytool in path_to_jre or in path_to_jre/bin
cd to keytool location
then run ./keytool
Make sure to add the the path to $PATH by
export PATH=$PATH:location_to_keytool
To make sure you got it right after this, run
where keytool
for future edit you bash or zshrc file and source it