According to the AWS documentation, you can't really do that...you can read it here - https://docs.aws.amazon.com/cli/latest/reference/ecs/register-task-definition.html
only by "Create new revision of Task Definition"Task definition -> -> create new revision
it will use the "latest" version in your repo (better to tag it with latest of course) or add the tag yourself.
BTW - I would use an automated process for these updates as part of ci/cd with json for that use, unless you already prepare to do so.