Hi @mohsen_ej,
You'll want to use the q2-cutadapt trim-paired plugin to remove primers from both your forward and reverse primers. Each should be on their respective 5' sites, this is why you don't see any repeated patterns on the 3' of your reads.
By default, your primers (if they are still intact) will be removed, and if they are not then nothing will happen. Those ambiguous N nts will be taken care of during denoising (as in reads with N in them will be dropped).
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