Hi @Hibabash et al.,
You can simply install the q2-fondue plugin and let it do all the work of preparing :qiime2: formatted data for you. 
Generally speaking, all amplicon data in the SRA should already be demultiplexed, as it is required that data be demultiplexed for upload to the SRA. The SRR/SRX/SAMN files usually contain sequence data from a single sample. If you'd like to download a bunch of samples from a given study, then you'll want to access via the BioProject ID or a list of SRRs.
-Cheers!