Press the menu button ☰ in the header bar.

Select Preferences.

Select the Key Servers tab.

Press the Add button.

In the new dialog, select the appropriate Key Server Type. Key servers are identified by the protocol they use to communicate. Look for the first few letters in the Internet URL of your key server to identify its type.

In the Host field, paste the Internet URL of your key server. Consult the documentation for the key server you're adding to see if it operates on a non-standard port. If so, enter the port after the ':'. If you're unsure, leave the text box after the ':' blank.

Press Save to finish.