In the year of migration a so called M form must be filed with the tax authorities. The M form is a complicated tax form. It combines a foreign period with a resident period. Whether income in both periods must be declared in the M form depends on the specific situation. Normally the M form will show a tax refund.
The M form can't be filed electronically, it must be filed on paper. Especially this type of tax form requires the assistance of a tax advisor. Expatax can of course assist you.