Hi @ramasravani,
If you wanted to import only the fasta files without the quality scores you would not be able to use denoising methods such as DADA and deblur and you would have to use OTU picking methods which are not ideal. With that caveat, you can import fasta files as per the importing tutorial here.
I am not experienced with mothur so I recommend asking for help on the mothur forum about this since this seems to be a question specific to that pipeline and not yet in Qiime2. My guess is you might have to take a step back and demultiplex again since your original files were actually in the right fastq format so there must be a way to demultiplex them without separating the qual scores. Alternatively, I had a similar situation and I outline in this post how I used qiime1 to demultiplex my samples before qiime2 importing.