Hello @Dali,
Welcome to the forums! :qiime2:
I'm glad you found that thread on conversion. I think it's a great resource! The answers to your questions are inside. 
The 3rd post by Luca is extremely important because converting from ASVs to OTUs is usually a bad idea that you want to avoid!!
Review that thread carefully, then report back here.
Do you understand why OTUs are usually worse than ASVs?
For your study, do you still want to use OTUs, and if so, why?
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