Applying a grayscale effect to a photo can be done using photo editing software or online tools. Here is an example of how to do it using Adobe Photoshop:

1. Open the photo in Photoshop.
2. Go to Image > Adjustments > Desaturate (or use the shortcut Shift + Control + U on Windows or Shift + Command + U on Mac). This will convert the photo to grayscale.
3. If you want to make further adjustments, you can use other tools such as the Channel Mixer under the Image > Adjustments > Channel Mixer or use different layer adjustments to get the desired look.

You can also try different methods to make Grayscale effect like:
-Duplicate the layer of your image, then go to the Layer>New Adjustment Layer>Black and White and adjust the sliders to get the desired look.

.Create a new layer in "Multiply" or "Overlay" mode and fill it with 50% gray.

It's worth noting that this method is for Adobe Photoshop, different software or online tools may have different options and method for applying Grayscale effect. If you're using another software, you can look for the grayscale option under the adjustment, filter or effect menu, or check if the software has a documentation or tutorial that can guide you through the process.