Need little help and suggestions from senior members

Hello every one !
i own a website which has 13 mil pages and only 600k page indexed i have good daily update sitemap and everything which i need to index my pages
i tried api and everything but its difficult to index all pages.
right now site:website.com showing only 5-6k page indexed
so is there any way i can use any auto tool such as rank x or money robot to buld back link and target all "discovered but not indexed " pages and if i do thatit will spam my site because its money site and its 15 year old domain

any suggestion will be help ful
thanks

Woo how come you generated so many pages. Is this PAA site ? Saw this AMA by @BlogPro try asking your questions.
https://www.blackhatworld.com/seo/b...s-job-boards-scraping-ai-ml-go-ahead.1415756/
I saw something related to index on this thread.

thank
its website related to RFP (government procurement) we edit and short all database and publish 100% uniqe and readable content on our website and people who participate in RFP they contact us and buy subscriptions