My transaction dissappears as soon as I click on it. Doesn't allow me to change tag.

Welcome to the Community, @karlaroberts125-. I have a few steps you can follow to help change the transaction's tag.

This may be caused by a corrupted cache file in your browser. This is one of its components that speeds up the loading process but there are times it gets corrupted resulting in odd behaviors. To determine, let's perform some troubleshooting steps. 

To start, access your QuickBooks Online (QBO) account using an incognito mode. This is a private browser that doesn't store cache and will give you a clean slate. Below are the shortcut keys you can use:'

• Google Chrome: Press CTRL + Shift + N.
• Safari: Press Command + Shift + N.
• Microsoft Edge: Press CTRL + Shift + N.
• Mozilla Firefox: Press CTRL + Shift + P.

Once signed in, attempt to open a transaction again to change the tag. If this works, go back to your regular browser and clear the cache to eliminate the damaged files. If you're unable to do so, I recommend using another supported browser or device. It might be that the current one you're using has a temporary problem with QBO.

I also added this helpful resource that you can access at any time to have guides and references in performing your QuickBooks tasks: QBO Help page. 

Please let me know how this goes and feel free to post again here. I'm always willing to lend a hand to ensure you can change the tag of your transactions. Have a good day ahead.