To help understand the 7-parameter transformation (translation + rotation + scaling) that’s involved in going from PRS 92 (ESPG:3123) to WGS84, study the section under the heading towgs84.
Emlid Flow doesn’t support the transformation between PRS92 and WGS84 now, but you can add it with a Custom CS. Please walk through this step-by-step guide from our docs to create it. For PRS92 / Philippines zone 3, you’ll need to choose the GRS80 ellipsoid and add the parameters for transformation and projection. You can find them by these links on epsg.org.