If you did a tax return for 2005 when you were there, would you not to the same for 2006 and 2007?
If you speak German, you can do it online at
https://www.elsteronline.de/eportal/. You need to download the elster software. Then you can decide whether you wish to print out your return, sign it and send it to the tax office, or if you want to sign it digitally. If the latter, then you also need to apply for a public key (or digital) certificate from Elster.
The whole thing costs nothing, and when you fill in your details into the Elster online application, it will calculate the amount of tax back you are due. It may not be 100% accurate if you've unusual circumstances. But you get a good idea of what to expect before you even submit your returns to the tax office.
Just remember that you need to download the correct version of the software for the year(s) you wish to submit tax returns for, as tax law (and therefore also the software) changes every year.
I did the whole thing myself from Ireland when I returned a few years ago. Submitted electronically, and the tax office got back to me asking me for proof of Irish income for the year (as I spent half of tax year here), so sent a copy of my P60. As I still had a German account, they then lodged the tax I was due back to that account. They should now also be able to lodge to any Eurozone account.