Call or visit your local technical school or community college and ask if they have any classes in using a spreadsheet in electrical estimating. If the school doesn't offer the training, perhaps it knows who does.
Hire a tutor. Advertise in professional journals for electricians and the local newspaper. Also put the word out on construction sites and with colleagues that you are looking for someone to teach you how to use spreadsheets for electrical estimating.
Look for online training on how to use electrical estimating spreadsheets (see Resources). E-learning is a popular way to learn particular skills, such as spreadsheet specific tutorials.
Invest in electrical estimating spreadsheet programs and do the tutorials that come with the software. Before you make a purchase, take a look at what others have to say and make your decision based on which package you think will best suit your needs (see Resources).