Yes, Mr. Weenie, we must go back to the modes and scales, at least for a quick replay of what is needed to be said. It won't take long, I promise. You might even learn something.
As you can see from the image, I've changed our sheet on Modes just slightly to list the flats (or sharp) that will go with each mode if you think of them in a major scale.
What? What you talkin' 'bout Willis!?
Well, the Ionian scale is basically a major scale, that's why there are no flats or sharps listed next to it on the sheet. We're going to base all of the other modes on the Ionian (or major scale), to help us find the others with ease and on the fly.
For example, it can be helpful to think of a major scale in relation to the whole and half steps it takes to complete the scale, i.e. whole, whole, half, whole, whole, whole, half.
But this gets much more convoluted when getting into the modes. For example, the Aeolian is whole, half, whole, whole, half, whole, whole. Who wants to keep that in their brain?
So, by taking the major scales (those scales we practiced over and over and over and over again when learning our instruments) and thinking of what flats or sharps with each mode needed to alter them - we make the chore of learning modes, much much easier.
So, let's go with the Lydian mode for a second.
Starting on F, we won't play the Bb so we're sharping the 4th to make it a B natural.
Now let's try a G Lydian mode.
If we look at the major scale, G has one sharp, F, but in the Lydian mode we will also play a C# to make the 4th note sharp (keeping with the Lydian Mode.)
See? Not that bad. When we memorize the differences in the modes based on the major scales, it makes a light chore out of some hefty lifting. You can teach an old dog new tricks... Right, Mr. Weenie?
Hope this helps!