Hello @israel,
Welcome to the forums! :qiime2:
EDIT: In 2024, here are newer pre-trained classifier for UNITE.
Here are the newest version I know about: UNITE (v.8.0 2018-11-18) Classifiers for QIIME2 Available Here
You may have to install an older Qiime version inside a separate conda environment to run this older pre-trained classifier. Let us know if you have any questions!