Hi @emiliomastriani,
Did you download the sequences form sra?
This previous question may give you some help:
A general point, I would import the sequences fastq files, possibly as paired-end, if you have those (in your case you seems to have both R1 and R2 in the same file, so you need a script to split them into two files).
For the import, please have a look at the "Fastq manifest format" in the import guide:
Importing data — QIIME 2 2021.8.0 documentation
Then you would need to join your sequences as described at:
https://docs.qiime2.org/2021.8/tutorials/read-joining/
After that, you can use vsearch plug in to cluster your sequences as your initial point (starting form dereplicating the sample):
https://docs.qiime2.org/2021.8/tutorials/read-joining/
Hope it makes sense1
Cheers
Luca