This assumes you already have GPG installed

Let’s say you have a pgp key generated on a device.

In my case I use OpenKeychain which lets you back up keys using the GUI, but on another system something like gpg --armor --export-secret-keys name@domain.com | gpg --armor --symmetric --output myKey.pgp.

In any case you will have your secret key and a password to go with it. Run:

gpg --decrypt myKey.pgp | gpg --import

You’ll be prompted for a password and you should be set.

Bonus: Raise trust

After importing a key you may want to raise the trust of your imported key.

Get the key ID: gpg --list-keys.

Lets say our key is 49VICCITSVUNYOWVG1VKOMPGW5RSW4E78TMW4YRA

Edit the key: gpg --edit-key 49VICCITSVUNYOWVG1VKOMPGW5RSW4E78TMW4YRA

Run trust, select your trust level. Then run save to save and exit.