The simplest way to install the correct release of Eclipse QVTo, is to use the Help->Install New Software... dialog, then to select the prevailing releases update site such as 2021-03 - http://download.eclipse.org/releases/2021-03 as the Work with target. Then type QVT Op as the filter text. You may then check QVT Operational SDK for a minimum binary-only install or QVT Operational SDK Developer Resources for the fuller SDK with sources. You may also check the corresponding Code Coverage support.
Alternatively you may choose to download an arbitrary milestone or nightly build by selecting one of the Update Sites listed below for use as the Install New Software... work with.
You may separate download and install steps, by first downloading the All-In-One Update ZIP. using the Download button below You may later use the ZIP for an offline install by selecting the downloaded ZIP as the work with.
There is a Marketplace Entry as indicated below, but it is often stale, and may allow you to install a mismatching version. This is really not recommended for Eclipse projects available as part of the Simultaneous Release.