Go on your groups main page and scroll down until on right side you see this click it.

Again on right side you shoud see Admin Tools and click on it

IF you have huge group just search the players in the box

Click on the cup and when it turns blue it the player will be set as Player of the Week in groups main page here is excample:

I am able to make more guides like this if you enjoyed this one and found it helpful. Giving this guide a good rating will tell me you want more.
Feel free to ask me questions in the comment section!

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