Please review my step-by-step Instructable, "Build a Tone Generator--Improve Your Snap Circuits by Adding a 555 Timer IC" (https://www.instructables.com/id/Build-a-Tone-Generator-Improve-Your-Snap-Circuits/).
Begin this build with the 555 timer IC tone generator circuit. See picture 2.
Parts Needed for build:
1 10uf Capacitor # 6SC C3
1 100 ohm Resistor # 6SC R1
1 1 Red LED # 6SC D1
Step 1. Replace 0.02uf capacitor C1 with 10uf capacitor and make sure the "+" is toward the whistle chip (see picture 3)
Step 2. Replace 470uf capacitor C5 with 100 ohm resistor R1 (see picture 3)
Step 3. Install LED D1 with the "+" toward the 100 ohm resistor R1
Here's a video to demonstrate the LED synchronized with the squarewave output of the tone generator: