Navigate to the title you want to patch using the searchboxin this site and downloadthe corresponding .txt patch depending on your region and/or disc revision.
In order to use WiiLink WFC, you need to have a NAND dump from a real Wii. If you don't have one, you can follow this guide to dump your NAND, then install it on Dolphin by going to Tools Manage NAND Import BootMii NAND Backup...
Right click the title you want to apply a patch to.
Click on "Properties".
Click on "Gecko Codes".
Click on "Add new code".
Paste the code you want to use in the "Code" field.
Save!