The easiest way to moisturize the vaginal walls with one of Astroglide’s water-based lubricants would involve pouring some onto your fingers and then slipping your digits into your vagina. You would then want to use full-length strokes in covering your entire vaginal cavity with lube, trying to get an even coat on all sides of the wall. If easier, approach the endeavor like you would in applying facial moisturizer, using the same application strokes.
Likewise, you could coat a wand-like sex toy, like a vibrator or dildo, with lube, in getting a better reach. (Note: a vibe will help to increase tissue strength, helping to improve your skin’s integrity.) An even better way to moisturize involves applying 1-3 ml using a needle-less syringe, preferably at bedtime. You should soak up all of the moisture overnight, but sleep on a towel in case you don’t.
Thank you for your question and good luck!