I want to convert the integer coordinates with the x and y coordinates to the coordinates of ED50. When I install the QGIS 2dhelmert plug-in, I get a 'missing metadata file' error. How do I solve this problem? Is there another method?
As far as I can see from https://plugins.qgis.org/plugins/helmert2d/ , the plugin was designed for QGIS 1.7.
Since then, the plugin API of QGIS has changed a lot, and the plugin will not work in QGIS 2 or QGIS 3.
Apart from that, you don't need Helmert 2D for converting coordinates to ED50. Just use
Save As ... and specify the CRS of the target file.