How can I correct gpx positions that are out of place?

I have a 12 hour plus track of our cruise through the Panama Canal.
Some of the individual positions, particularly while in the various
locks, where the movement horizontally was 0, while there was a
vertical movement, show up as zigs and zags over dry land. My
suspicion is that over the course of the time the ship was going up or
down the connnection to the satellites was changing, as one moved out
of range and another came into range, resulting in shifts of the
position recorded. What I am looking for is a bit of software that
would allow me to look at the track, select an individual point along
the way, and DRAG it from dry land to being where the ship was in the
lock, and then allow me to drop it in that location and update the
record to eradicate the error. I have several dozen such points and
doing it manually via an edit to the text in the gpx file is a tedious
exercise. I know that IS an alternative, but I much prefer to be able
to drag and drop the incorrect locations into the correct locations,
and THEN geocode the photos I took while traversing the canal.

Does anyone know of an piece of software that will permit that sort of
movement of individual positions in a large GPX file?

TIA

RsH