Interesting side of this pandemic. A lot of entrepreneurship.
I have been involved on acquiring brands. It’s only as easy or difficult as the people behind them. There’s no one size fits all approach.
so you have to approach the current brand holders and see where they are at.
taking this particular case aside You normally find:
1- brand is gone and you just have to deal with paperwork cost
2- brand stakeholders are willing and happy to deal and their personal level of wealth will determine their need to make an extra dime from you.
3- they love your idea and will either partner with you or
4- steal it from you.
in the latter two cases your record on actually achieving something may determine the outcome. Not necessarily on a straight forward way. Sometimes the idea that someone may achieve greatness out of their brand will set a fire going on their bellies.
So, be ready for all Possibilities. In your case the success of failure of Eterna may affect their current brands so they may prefer to park it until they are ready to do something for it.
first approach is hire lawyers to research the copyright and status of the brand. ( sometimes businesses forget to file paperwork)
second assess interest on selling without disclosing your intent.
You don’t need to “sell “ them on anything because if you do... then they have the power and control to buy the whole thing away from you.
last, if they just are not interested on selling; You can approach them with a business plan and concept where they could partner with you. Before that point consult a copywright and trade legal team
To see what portion of your concept, if any, can be secured to you.
I don’t see any of the described points that would fit that bill but I’m not a lawyer.
BUT, if you have a cool plan, a good team that can execute or has a proven record... then I have seen times where a brand holder has partnered or given control to someone to elevate a concept.
Good Luck.