I know about a medium sized business (deals with grinder blades manufacturing) which is operating in

I know about a medium sized business (deals with grinder blades manufacturing) which is operating in a shady way and doing tax evasion/ showing less purchases on paper to avoid taxation and doing majority of purchases and selling finished goods without bills to avoid paying tax. The owner and son have been doing this for quite a long time. They can’t put this money into bank since there’s no trail of it so they have lots of cash in house or factory or put it into different committees (I particularly don't understand working of committees, so won’t comment). I know the details of owner, contact and location of manufacturing (not exact but the area yes). nI wish to file an anonymous complaint to tax department to look into their finances and business and bills, numbers won’t match. I don’t want to get into trouble in any way or form so I wish to do it completely anonymously. Help me with the procedure please.