Dead nettle is a common lawn weed. Its seed can blow in from other sites, birds can 'deposit' the seed their poop, or the seed can be brought in with soil or mulch brought into your yard.
Once it is growing as a plant in the lawn and gardens, a broadleaf weed killer will be needed to chemically remove it. Or you can hand dig it out.
UConn Home and Garden Education Center
Thank you for your response. I will tackle the job to get rid of them