With the Live Editor you can generate the minifaces for your players. The tool is using the Player Capture System created by EA that game is using for generating the miniface for your created player or homegrown talent.

If you want to use custom picture, check the Importing Miniface Guide

To open player editor:

• Run the FC 26 Live Editor. (Getting Started Guide)
• Load the game mode where you want to edit player
• Press F9 on your keyboard to open the menu
• From Features click on Players

• Find Player and Click on Edit icon to start editing him

• You can now edit the player.

• When you are in player editor click on Player -> Miniface -> Generate Miniface

• Where the generated minifaces are stored?
  • By default the minifaces are stored in C:\FC 26 Live Editor\mods\legacy\data\ui\imgAssets\heads and C:\FC 26 Live Editor\mods\legacy\data\ui\imgAssets\youthheads

• How can I delete generated minifaces?
  • Simply by pressing Delete miniface in top right corner in player editor, or by deleting the file from C:\FC 26 Live Editor\mods\legacy\data\ui\imgAssets\heads and C:\FC 26 Live Editor\mods\legacy\data\ui\imgAssets\youthheads