This is a really difficult problem, due to the curved side. There are 3 basic methods I use for this. (1) Make a frame out of wood. It would need to have groove on the underside that fits securely over the tank rim. But making a curved piece of wood with a perfectly curved groove is something that only a very talented woodworker could get right. (2) Get "Industrial Strength" velcro of the adhesive kind, and sew-on velcro of the non-adhesive kind. Put the "soft" side of the adhesive velcro on the tank rim. Sew the "rough" side onto the screen material. I have done this, and it works very nicely... but... the cost of the velcro is much greater than if you simply... (3) Buy a screen lid.
For this type of tank, option 1 required difficult woodworking, option 2 requires difficult sewing, and option 3 may be a product that does not exist (I've never seen any screen lids sold for bowfront tanks).
As an alternative, does the glass lid have any cut-out areas that would allow you to put a tiny fan over the tank? I'm thinking of these little computer-type fans that they sell now for installation over aquariums.