Exporters of service

Dear experts
we do software development projects for foreign clients and we receive payments from them in dollars .we also do some projects for our indian clients and our aggregate turnover crosses 20 lacs . our query is what is the procedure for submittin g letter of undertaking for exports without payment of gst.is the form available on common portal??.
Further we have already done some export services to foreign clients we are not yet registered on the notion that we are below 20 lacs how do we deal with these turnover from export of services before registration?? should we declare it in the first return??