.. ..... get hold of the next size up and you might be able to hammer it into the damaged socket in the screw.
PS. TIP 3.
If you do go down this route .......... once the larger bit is jammed into the rounded off Torx socket, do not use a small ratchet lever, or other means where by sideways pressure is applied to the Torx bit. Use a small socket and T Bar, ..... By using the T Bar, you will only apply rotary motion to the Torx bit and there won't be any sideways levering which tries to lever the bit out of its socket and in doing so damages the mating surfaces.
The same principle applies when unscrewing bleed nipples. I always crack them first with a socket and T Bar. If a small spanner is used there is a high degree of shearing motion which, if the nipple is tight, tends to lead to a sheared nipple.
Below is a pic of what I do when cracking a bleed nipple. This was on my Sirion and the nipples where tight but with this method there was a loud crack when they released, and they then unscrewed without damage.
I know that a bleed nipple is not quite the same, but the basic principle applies to tight Torx screws.

1990 GTA Atmo, 2003 Jaguar X type 2.5SE Auto, 2018 Kia Picanto GT-Line-S 1.25