Many people hold their right arm up from the shoulder (where else?) and
then push down on the bow to get bow weight on the string.
There is another way that takes less effort and is a steadier weight.
With your bow on the string, you relax your shoulder muscles somewhat,
and then twist your wrist counterclockwise and twist your arm so that
it tends to hold up your arm via the bow instead of from your
shoulder.
You can have someone hold your arm while your bow is on the string,
then relax your shoulder so your helper is really holding up a lot of
your arm weight. Then twist with your wrist and arm to transfer
some arm weight through the bow and onto the string. Your helper
should be able to feel when your arm weight decreases on them.