There are 2 steps to answering this question :
1. Clarification - What sort of blue-collar workforce are you dealing with - Industrial or domestic? Which side of the blue-collar hiring product are you looking to make - Supply-side or demand side, i.e. a product for companies/individuals who are looking to hire a blue-collar workforce or a product for a blue-collar workforce to get hired? Is it a marketplace model or more like a recruiting agency that takes care of many services such as background checks, workforce management etc? What is the target geography? Depending on these answers, your GTM and business model can vary hugely.
2. Solution - Let's assume that you are building a marketplace of the domestic blue-collar workforce in India, Delhi, (select specific residential locality) so that individuals can hire them. What are the major classification of such workforce in India? Start understanding the persona of such individuals. The problems faced are security, work quality and cost. If you had to reach out to such individuals and build awareness about your product, where would you begin with? How would these individuals be sure about the work quality? How can you make money out of this business because an individual would hire a domestic worker for at least 1 year? Keeping all the above factors in mind, for V1 :
Business model -
Demand-side: Feature the domestic workforce based on their capability such as Household work, Cooking. You would feature a workforce whose background has been verified. You will mention the approx cost range because a house could have 2 bedrooms or 3 bedrooms or the family could have 2 people to 10 people. You will provide a 1-day free trial to build confidence with your customer. Once the customer finalizes the domestic help, you will charge a one-time placement fee - 10% of her monthly salary.
Supply side: Engage with the workforce community and get feedback on domestic help. Educate them on how they can earn more money through your product.
GTM strategy -
Begin with duct tape online marketing by figuring out relevant facebook groups and engage. Understand how people in those specific areas find the domestic workforce and begin marketing through those channels. If the persona and practices reflect usage of google for domestic services, you can purchase Google AdWords too.
The idea is to enter the blue-collar hiring but with a minimal cost. Once you have the product market fit, you can pour money on marketing, strengthening services, new features etc.