The fight with the Gnolls isn’t hard if you take advantage of the terrain. There designers put a ledge right over them for a reason.
I dunno, I've tried to use the cliff and the archers still just murder me. 3 attacks/round, doesn't reallly matter what your AC is, they are gonna hit you.
I usually have Asterion hide and sniper a few with his sneak attack longbow until they get wise, then he cunning dashes away while shooting behind him until I train them all the way back to just outside Wakeen's rest where I can bottleneck them, problem is sometimes the game just glitches out and they teleport to the cave and kill the Zentium.
There are actually three fights with gnolls, seemingly you especially refer to the third? Of course tacticts are related to your group. My party at that time (lvl 3) regularly consists of Shadowheart, Gale, Wyll, my PC is currently a ranged Fighter while normally I'm playing as Barbarian. If your PC is Priest, Sorcerer, Wizard or Warlock, it's equally easy, for the rest I don't have much experience (the first class I played after EA release was Ranger, I found him a bit weak).
The first fight you should try to avoid by killing the hyenas before the gnolls come out. If I fail, I make it a running battle back to the bridge, so that some chars always are in safe distance.
The second fight (4 gnolls on the hill) I start from stealth by using Grease spell. Stealth is quite broken, so you can fire with all chars at the poor gnolls. I have Shadowheart at the far distance, to be able to raise downed chars with the best spell in the game, Healing Word (she is the only one who can use it, as I never use scrolls). It's usually not even necessary to fire your good spells, I just use cantrips or crossbows for Shadowheart and Gale, except I'm very unlucky. So I don't have to long rest before the third gnoll encounter. BTW if you have a companion with a minion, use it to offer a target for the gnolls, they are dump as hell.
The third fight is the most demanding, but also not such a problem. I also start from stealth. I position Gale and Wyll on the rock on the left in front of the gnolls, Shadowheart on the right side, then I sneak to the boss gnoll and attack. You can fire with all chars because of stealth. The gnolls usually try to attack my PC who is near the boss gnoll and stand all near to each other. A perfect opportunity for Gale to use Shatter. If the archer gnoll on the high hill on the right side attacks from above (sometimes he comes down, the fool), I deal with him by shoving him/it away, either with Wyll's Eldritch Blast or with a Battlemaster die. If you are in the unlucky situation to have none of this available, you should sneak one of your chars up the hill before the fight. In the worst case you can Misty Step with Gale and blast the gnoll away with the blast wave spell.
