How to convert this equation to y=mx+b form:
y+2x=y-2

Y = mx + b is in the form of slope-intercept.
From the equation given, y + 2x = y - 2, we can convert it in the format of the slope intercept form and it depends we can came up to that form.

y + 2x = y -2
y - y = -2x - 2
0 = 2x + 2
x = -1

Unfortunately, the form y = mx + b is impossible to achieve.