Alternative to Climbers and Renegade Rows?

The workouts on Darebee are okay - I like their illustrations - but as with most fitness websites, the sorting/leveling is really hit-or-miss. It's really hard to find true "beginner"-level exercise routines; the vast majority of workouts labeled as being for beginners assume a base level of fitness that for many of us is simply not there.

What are you looking to get out of this exercise program? Are you aiming to build core and back strength specifically (both of these moves target the abs and shoulders)? Or are you just trying to move more in general?

Bird-dogs are a good sub for the mountain climber if you can get on hands and knees (also called "tabletop" position - knees hip-width apart, hands shoulder-width apart, flat back). You extend one leg straight behind you and the opposite arm in front of you, then return to the start position and switch sides. It might be challenging enough to just hold the position for a few seconds, but if that's too easy, you can add the crunch variation where you curl inward and bring your elbow and knee together.

If you're not up to hands and knees, deadbugs also target the abs with a similar movement. Lay on your back, arms straight up like you're reaching for the ceiling, knees bent 90 degrees and legs raised. Extend one leg and bring the hand on that side down toward your hip, while lowering your other hand up over your head, then return to the start position and switch sides.

Renegade rows look impressive but it's not strictly necessary to train both abdominal stability and the upper back at the same time, unless the specific thing you're trying to get good at is renegade rows. Regular-*kitten* planks are probably plenty challenging for your abs at this point in time; if it's hard to do them on the floor, you can do them on an incline (your hands higher up than your feet, on a wall/counter/stair/furniture - anything that will support your weight without tipping or sliding when you lean on it). If you can hold a plank on an incline for a minute or so, you can up the challenge by reducing the incline; if you can plank on the floor, try tapping one arm or shoulder with the other hand, switching back and forth. Go slow, you don't want to rock or sway, you don't want to build momentum here. Imagine there's a glass of water or a tennis ball on your back that you don't want to fall (or have someone put something on your back that won't be dangerous if it falls off of you, like a tennis ball or a soft toy).

If you're more concerned about training upper body, there's a million and one ways to do rows. The most basic variation if you're using dumbbells at home is probably the bent-over row, using one arm at a time or both. For one arm, you want your feet staggered in front and behind you. Bend your front knee and prop yourself up with that arm. Dumbbell in the other hand, the motion is similar to starting a lawnmower (but slowly and with control) - start with arm extended toward the floor, pull the dumbbell straight up toward the shoulder, then lower back down (again slowly and with control, don't just drop your hand). Repeat as many times as you want to, then switch sides.