I updated QGIS and accidentally rewrote 2.18 as ltr with 3.4 Madeira. My apps work with older version. This means there must be qgis-full and qgis-ltr with version 2.18 to make them work correctly. How can I restore my previous installation or find packages for installation from local folder. I use Windows 10 64 bit.
You can download older versions of QGIS here:
2.18 is however no longer supported. So there will be no more bug fixes. 3.4 is now the ltr release.
So my comment wasn't quite correct. You can still install QGIS 2.18 through the OSGeo4W installer, it won't be the LTR, since it is not the LTR. But it can be installed. You just need to untick "Hide obsolete packages":