You can also find all the clips you made yourself by clicking your profile picture in the top right, selecting Creator Dashboard, clicking Content in the left menu, then Clips.
The content of this reel can be likewise irreversible.
Twitch clips have an aspect ratio of 16:9, while TikTok videos are displayed in 9:16, so I recommend.
All you have to do is click Local File and then select the file from your file browser to upload it to stream ladder.