According to website of the municipality of Rotterdam on the decree on assistance for the self-employed (BBZ):
As for the special scheme announced by the Department of Employment two days ago, there is still no application information. On 26 or 27 March, the municipality of Rotterdam expects to have more clarity and an application form for the Ministry's scheme.
Please note the Rotterdam municipal website: https://www.rotterdam.nl/werken-leren/coronam measures-rbz /
The company does not exclude that other municipal authorities will also announce on this date. Keep an eye on your hometown news or website.