How to get ASV_ID

I use dada2 get a feature-table.It's first rowname is OTU_ID.How can I get ASV_ID?

Welcome to the forum!
In this case, your ASV IDs will be OTU_IDs. Actually it is just format specific name of the column and since you obtained a feature table from Dada2 plugin, you have ASVs instead of OTUs.