You need to know the length of the DNA to do this conversion. There are plenty of online calculators you can use.

this is excerpt from one of my methods papers: "The eluted purified DNA fragments concentration (ng/μL) was measured by Implen NanoPhotometer® P330 (Implen, Munich, Germany). Using the molecular weight of each fragment based on its sequence (as by Stothard, P., 2000. The sequence manipulation suite: JavaScript programs for analyzing

and formatting protein and DNA sequences. Biotechniques 28, 1102–1104.) approximate number of its copies per 1 μL was calculated using a DNA copy number calculator (https://www.thermofisher.com)."

But in your case, you only need to know the length (and ideally the actual sequence) of the fragment, and simply calculate its molecular weight, this gives you the weight of single copy (don´t forget to calculate for dsDNA). hope it helps.