gpg --edit-key 'Your key'

gpg (GnuPG) 2.2.4; Copyright (C) 2017 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

sec  rsa4096/0xF759E5159BD8ADB0
     created: 2017-07-13  expires: never     usage: SC
     trust: never         validity: unknown
ssb  rsa4096/0x0FDF21CEA632F8D7
     created: 2017-07-13  expires: never     usage: E
[ unknown] (1). Name Surname <email@address.com>
gpg >

trust

Please decide how far you trust this user to correctly verify other users' keys
(by looking at passports, checking fingerprints from different sources, etc.)

  1 = I don't know or won't say
  2 = I do NOT trust
  3 = I trust marginally
  4 = I trust fully
  5 = I trust ultimately
  m = back to the main menu

Your decision?