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Do you still have the card you purchased, or did you use it and register your nuvi with a garmin account. If you did then it should be connected to your email.
If thats the case, then all you need to do is download the garmin express program from here. And then install it
Then, connect your Garmin to the computer, turn it on. Garmin express should recognize it, and then it will prompt you to install the software, and map updates.
If you get stuck or run into any issues, let me know.
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Senior Technician and Network Switching Systems Operator / Maintainer.