Map lookup column with another column

Hello there. I have 2 SP lists. One is like an equipment inventory with items and the other one is for orders.

So, inside the orders SP list I created a lookup column to the equipment SP list to get the title and get multiple items in that list. My question is how can I relate this lookup column with another column in the orders SP list?

Think of you creating an order. Inside the order you add 3 items from the equipment list (from the lookup column) but for each item you added you need to specify quantity. How is this possible?

Using online SP in modern design

Thank you