First step is go to your profile edit page: http://gtm.steamproxy.vip/my/edit

When you are in there, press CTRL + SHIFT + J

A console should open up, you are ready to head onto the next section of this guide!
Favorite Game Showcase
For the favorite game showcase (the single game with all the details), edit the AppID in this command and paste it in to the console.

FavoriteGameShowcaseOnGameChange( this.parentNode, 6, 0, {appid: 00000})

Once that is done, press enter and save changes to your profile.
Game Collector Showcase
For the game collector showcase (the 4 games side by side), edit the AppIDs in these commands and paste them in to the console separately.

SetShowcaseConfig(2, 0, {appid: 00000}) First game (from left to right)
SetShowcaseConfig(2, 1, {appid: 00000}) Second game (from left to right)
SetShowcaseConfig(2, 2, {appid: 00000}) Third game (from left to right)
SetShowcaseConfig(2, 3, {appid: 00000}) Fourth game (from left to right)

Once that is done, press enter and save changes to your profile.
Some special AppIDs you could use
http://gtm.steamproxy.vip/groups/SteamTricks2/discussions/0/1291817837622039104/
this games app id - 657880

All credits go to original guide creators, posted here for educational purposes.

Greenlight - AppID=765
SteamVR - AppID=250820
Steam Cloud - AppID=764
Steam (Client) - AppID=753
Steam Music - AppID=258280
Steam Economy - AppID=754
Steam Artwork - AppID=767767
Steam Screenshots - AppID=760
Steam Cloud - Videos - AppID=761
Steam Cloud - User Logs - AppID=764
ValveTestApp200269 - AppID=200269
Steam Controller Configs - AppID=241100
Steam Software Beta Access - AppID=218800
Game Library Sharing Access - AppID=248210
Steam Trading Card Beta Access - AppID=202352
Beta Access to the New Steam Community - AppID=202351
Steam Workshop (No playtime will be displayed on Profile) - AppID=766
404 ERROR 65120
NAVI : 413856
FLIPSIDE: 413857
CLOUD9: 413851
VIRTUSPRO: 413852

From here:
https://gtm.steamproxy.vip/app/657880/discussions/0/1736588252384073927/#c1743346190275687364