While it may not be possible to revert the color conversion directly, you can try to manually adjust the colors in the edited PNG file to match those in the original PSD file as closely as possible.
If your PSD file doesn't have any layers and doesn't contain a color profile, then the color information in the file is likely in the default color space of your editing software (often sRGB).
When you saved your edited PSD file as a PNG with the "Convert to sRGB" option checked, it means that the colors were converted from whatever color space they were in previously to the sRGB color space. This conversion is typically not reversible, especially if the original color space information is not preserved in the PSD file.
However, you may be able to minimize the color differences by manually adjusting the colors in the edited PNG file to match those in the original PSD file. This process can be time-consuming and may not yield perfect results, but it's worth trying if the color differences are noticeable and problematic.
Alternatively, if you have access to color management tools or software (Photoshop actally works), you may be able to analyze the color profiles of both the original PSD file and the edited PNG file to identify the differences and attempt to match them manually.
Let me know if it worked.