I suck at slogans, but...

"You like this service? Our founder came to the US in 19XX"

"You enjoy this website? Here's a list of 2nd generation immigrants on our executive board"

...might get people to realise how much of the US economy is driven by 1st & 2nd generation immigrants.

That won't help change attutiudes. It will reinforce existing attitudes.

"See! Immigration is good. These immigrants and their kids are building services!"

"See! Immigrants are hiring other immigrants and their children to provide lower cost labor and networking out-of-country and locking us out of the market."

If you want to change, you need a slogan like

"American made, American owned, American labor." along with the (now disappearing) attitude that American is not an ethnicity, it is a lifestyle.

I am not sure that legal aid/advocacy will help those affected here. The President has wide latitude to make immigration decisions. Love it or hate it, the new policy is what it is and the courts are likely not in a legal position to be able to overturn or make an end-run around it, regardless of how compelling the argument in a given case is. Encouraging new and timely legislation is much more likely to be effective if you are opposed to this executive order.

It helps in three really important ways:

1) You don't have the right to counsel in immigration hearings. There are several organizations that provide free legal aid.

2) Immigrant communities are scared and need to know their rights, and have a trusted source of information. There are unfortunately a ton of scammers who prey on scared people.

3) These organizations are a helpful intermediary between vulnerable people and government agencies, police, etc.