Simple, mostly stolen script from one of pr in official gc, which allows to quickly change traveller element.
Original pr: Grasscutters/Grasscutter#1287
I just added dendro and changed it to plugin.

Use /se or /switchelement
Elements: white/anemo/geo/electro/dendro
white = no element

For dendro you need to have:

1. Genshin 2.8.5 beta
2. Grasscutter supporting that version
3. Dendro files from Endg4me_#7769 (From here if you're in Frontrooms)

I don't know why would you want to build it but:

1. Download maven from apache website
2. Open command prompt/powershell in your project folder (Sorry Linux and MacOS users, you'll need to find your own way for this)
3. Run mvn package
4. Now jar file should be in new target folder

The plugin is based on plugin template from Grasscutters GitHub.