Cities are increasingly challenged by extreme heat events, which pose serious risks to public health and urban livability. Micromobility users, whose numbers have increased rapidly in recent years, are particularly vulnerable to outdoor heat exposure. Yet, their exposure patterns and the effectiveness of mitigation measures remain poorly understood. Here, we couple a high-resolution urban microclimate model (WRF--BEP--SOLWEIG) with 4.76 million Citi Bike trips in New York City to quantify cyclists' thermal exposure during the June 2024 heatwave and to evaluate targeted cooling strategies. Results show that a small fraction of the street network concentrates the majority of rider heat exposure, and that localized interventions along these segments yield the greatest benefits. Targeted tree planting along just 1.5% of the city's street network reduces total heat-exposed kilometers ridden by 19%, equivalent to a thermal stress reduction of about 4°C, with its impact maximized during midday hours. In contrast, randomized citywide tree planting produces diffuse, resource-intensive cooling, highlighting the superior efficiency of spatially prioritized interventions. Baseline results further indicate that daytime heat stress is higher in lower-income neighborhoods, adding an important social dimension of urban heat exposure. Together, these findings provide a quantitative basis for designing heat-resilient and equitable cycling networks in a warming climate.