Tips for going into lugia battle?

my team is underleveled as all hell, and can barely scratch lugia, no less get outsped by it (my highest leveled mon is a level 50 heatmor, and it doesnt even do more damage than its leftovers heals). what are some good places to train a team to get to a decent level, say around 50 give or take? thanks in advance.

also, my team is: steelix, serperior, mightyena, claydol, donphan, and heatmor. only reason why theres 3 ground types is that i only use mons i get attached to, and i was unfortunate enough to get attached to 3 ground types

I would try to rework your team as soon as possible, as although it might be hard for you, it will most certainly make it easier when you go into the E4 which is a nightmare for some people, especially since no amount of grinding will help, unless it is to get it all to the same level. I get that it might be hard to box some of the your pokemon as I sometimes have that same problem, but it will make the whole game a bit easier if you change the pokemon around a bit.

Your current team seems to be lacking coverage for water, normal, dragon, dark, flying and ice and this could potentially be a problem.

A good way to grind levels is with the level trainer in your secret base, probably also using the lucky egg and some exp shares. It might also be worth starting to ev train some of your pokemon

If you want, I might be able to trade you a donphanite as the ability lets you hit types that would usually be immune to the attacks for example, you would be able to hit lugia with earthquake even though it is a flying type.